This invention concerns weaving machines with an improved weft thread supply, more particularly weaving machines of the type in which each weft thread remains attached to the edge of the cloth between successive picks, as for example on rapier weaving machines.
It is known that the weft thread supply on certain types of weaving machines, such as rapier machines, includes one thread preparation mechanism for each type of weft thread, plus a thread presentation mechanism for presenting the respective weft threads in the path of a feed gripper. The thread preparation mechanisms each include a thread package, a prewinder mechanism and a thread braking device.
From Belgian patent No. 901.969 it is known for a thread detector to be included in the thread preparation mechanism. The thread detector is connected to the control unit such that whenever a broken weft thread is detected in a corresponding thread preparation mechanism, the machine automatically switches to another thread preparation mechanism, so that weaving can continue.
On rapier weaving machines in which the weft threads are cut loose at the beginning of their insertion after being presented in the path of the feed gripper, and then after insertion remain attached to the thread package back from the cloth edge until a new insertion of the corresponding weft thread occurs, the abovementioned method of automatically switching between thread preparation mechanism poses a problem. On such rapier weaving machines, the weft threads are drawn along with the cloth at a constant, if low, speed. This means that if a thread break occurs in a thread preparation mechanism, the section of thread still attached to the cloth edge is eventually drawn out of the thread preparation mechanism and falls into the path of the rapier. Such a section of weft thread is then carried into the shed along with the next weft thread to be inserted, so that a fault occurs in the cloth, of a type which is difficult to detect by conventional weft detectors.